Gas Giants and how they form in the Universe
By : John Whitworth / Updated : Jul 17th, 2026 19:22
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Gas Giants are massive planets made mostly of hydrogen and helium, such as Jupiter and Saturn, while Rocky or Terrestrial planets like Earth have solid surfaces. To be classed as a planet, an object must orbit a star, be spherical, and clear its orbital neighbourhood. Dwarf planets fail the third requirement.
There are two main types of planets in the Universe, the Gaseous Planets, normally called Gas Giants on account of their size. An example of a Gas Giant is Jupiter, which is the largest planet in The Solar System.
The second type are Rocky or Terrestrial Planets of which Earth is a prime example. Dwarf planets are a subsection of these. An object must pass three specific tests to be called a planet. The tests are as follows:-
- Orbit a star not a planet.
- Have enough mass to be spherical.
- It has cleared its neighbourhood as it orbits its star.
All the planets that have been classified as a Dwarf Planet, such as Ceres and Pluto, are rocky objects. They fail the planet test because they have not cleared their path as they orbit our star. Some see it as a fudge to downgrade Pluto so that we don't have a tenth planet in our system when Eris was discovered.
There's nothing in the rules to say that a Gaseous Planet can't be a Dwarf Planet instead of being just a Planet. No Gaseous Planet in other Solar Systems has been discovered yet, but that doesn't clear its neighbourhood. All the Gaseous Planets in our Solar System clear their neighbourhood.
Gas Giants have been referred to as failed stars because they are similar in makeup to a star but have insufficient mass to start nuclear fusion. Nuclear fusion in stars is the process by which hydrogen atoms fuse to form helium and heavier elements. When a star is in the Main Sequence of its life, it is doing Nuclear Fusion.
The current smallest star, EBLM J0555-57Ab has more mass but is smaller than Jupiter. Had Jupiter a little more mass, then we would be in a binary star system like that of Tatooine in the Star Wars series of films.
The first planet formed in our Solar System is believed to have been Jupiter, according to scientists. Scientists have found evidence suggesting Jupiter was the first planet in terms of chemical composition. A.O.L.
Four gaseous planets in our Solar System are on the system's outskirts. The Gaseous Planets are:-
Gas Giants: Fast Facts and Characteristics
- In the Solar System, we have four Gas Giants, alternatively known as Gas Planets.
- The Largest planet in the solar system is Jupiter, a gas giant.
- The Largest planet in the solar system is Earth, the planet we live on.
- Large rocky planets are normally called Super-Earths, which we've found orbiting other stars.
- Large Gas Giants bigger than Jupiter orbiting other stars are called Super-Jupiters
- The larger the planet, the stronger the gravity. On any planet that is larger than our Earth, astronauts, if they ever made it, would very well have difficulty coping on the planet.
- All the gas giants in our Solar System have rings.
- All four outer planets of the solar system are Gas Giants
- Gas Giants may have a solid core, but no one has seen it yet; they have only theorised.
- The smallest Gas Giant Planet in the solar system is Neptune, which is also the furthest from the Sun.
Deep Inside: Atmospheric Layers and Composition
Although a Gas Giant is predominantly hydrogen and helium, it probably also has a rocky core. Outside the rocky core is a liquid shell, and the gaseous atmosphere is above that. No one has seen the core of a Gas Giant, but it is assumed that there is one.
A liquid or central rocky core is one reason you couldn't fly through a gas giant. Even if we had the technology, the stress and pressure would be immense, making it a bad idea. N.A.S.A.
Bespin
We all remember Bespin from Star Wars. If not, here's a refresher. Bespin was the Gas Giant in Star Wars V - The Empire Strikes Back whose Cloud City was administered by Lando Calrissian. It was where Han Solo sought sanctuary from Darth Vader. Hopefully, it is coming back to you now.
It is not without possibility, but more unlikely than likely that a Bespin-type planet exists. For a Gas Giant like Bespin to exist, it must have an Oxygen atmosphere. Still, oxygen is heavier than hydrogen or helium and would be found at lower altitudes than you saw in the film, rather than in the upper atmosphere. You'd be hard-pressed to find a Gas Giant with breathable air, and probably not want to waste your time finding one.
Is Life Possible Within a Gas Giant?
Could life exist in a Gas Giant atmosphere that didn't need oxygen? It would be extremely tough to survive in the atmosphere. Life has survived in the most extreme of places here on Earth. Life, such as organisms (viruses and bacteria), would have the best chance of survival. Life on Earth needs oxygen, but life elsewhere could need a different gas to survive.
Whilst life, like us humans, needs a firm, solid ground to walk on, bacteria would float in the air. Sharks in the oceans don't need to touch the ground. If they stopped moving, they'd die. A shark-like animal (one that doesn't need a solid surface to move on) could survive in a gaseous atmosphere.
You'd probably better off looking for life in The Moons that orbit a gas giant. There are theories that life exists on The Moons of Europa or under the ice of Io. Life needs heat to survive, and the Gas Giant the planet orbits would generate that heat.
Hidden circles: The ring systems of the Outer Planets
Apart from being gaseous, all the Gas Giants in our Solar System have rings like those of Saturn, which is famous for its rings. Jupiter's ring system is faint, and it was only discovered when a Voyager Space Probe flew past it. None of the Rocky Planets in our Solar System has rings.
Scientists announced in 2012 that they had found rings around an exoplanet in the constellation of Centaurus in the southern hemisphere. Whilst the official jury is still out, as more investigation is needed, it is interesting or disappointing (depending on your viewpoint) to think that our Gas Giants are not special. The planet would be 5 to 20 times Jupiter's size due to the rings' size. SyFy
Planetary migration: How gas giants move
When we look at the Exoplanets in orbit around other stars, we see that many are very close to their star. The Gas Giants are believed to be born far out and then migrate inwards. The Gas Giants of our Solar System are on the outskirts, but they could be migrating.
According to scientists at Lund University, Sweden, Jupiter was born four times further away from its current position and has migrated towards its current location. The world won't end anytime soon if the migration continues. If the migration does continue, it will be a very long time in the future before we see anything obvious. The evidence of this can be seen in the asteroids around Jupiter. Lund University
Beyond Our System: Super-Jupiters and Exoplanets
If you think that Jupiter is the biggest planet that could exist, then you'd be wrong. Some exoplanets are out there that are much larger than Jupiter. They are known as Super Jupiters. Some Super Jupiters are possibly Brown Dwarf Stars and therefore can't be classed as a planet. The current largest Super Jupiter is in orbit around KR Muscae in the southern celestial hemisphere and has a radius of seven times that of Jupiter. Wiki
